A130202 Odious triangular numbers.

1, 21, 28, 55, 91, 171, 253, 276, 351, 406, 465, 496, 595, 666, 820, 861, 1081, 1225, 1378, 1431, 1485, 1540, 1653, 1770, 1891, 2211, 2346, 2485, 2850, 3003, 3160, 3240, 3403, 3655, 3916, 4186, 4371, 4560, 4753, 4950

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)

Formula

a(n) = A130201(n)/2. Multiplication by 2 preserves odiousness, hence this sequence is odious oblong numbers divided by 2.

Mathematica

Select[Table[n(n + 1)/2, {n, 100}], OddQ[Plus @@ IntegerDigits[ #, 2]] &]
Select[Accumulate[Range[100]], OddQ[DigitCount[#, 2, 1]]&] (* Harvey P. Dale, Dec 04 2016 *)

Crossrefs

Cf. This sequence is the intersection of odious (A000069) and triangular (A000217) numbers.

Sequence in context: A048012 A254368 A276674 * A162692 A048067 A344603

Adjacent sequences: A130199 A130200 A130201 * A130203 A130204 A130205

Keyword

nonn

Author

Tanya Khovanova, May 16 2007

Extensions

Offset corrected by Amiram Eldar, Dec 09 2019

Status

approved